The present invention relates generally to integrated circuits, and in particular to delay locked circuits.
Delay locked circuits reside in many integrated circuits for delaying an external signal to obtain an internal signal. The delay locked circuit automatically tracks the external and internal signals to keep them synchronized. The internal signal usually serves as a reference signal for the integrated circuits instead of the external signal because the internal signal matches internal operating conditions of the integrated circuits, such as process, voltage, and temperature, better than the external signal does.
One type of delay locked circuit measures a timing of the external signal in every cycle (period) of the external signal. Based on the measurement, the delay locked circuit adjusts the delay applied to the external signal to keep the external and internal signals synchronized.
In many cases, the operating conditions of the integrated circuit remain unchanged for a time substantially greater than the cycle time of the external signal. Therefore, measuring the external signal to adjust the delay in every cycle time of the external signal wastes power.
Various embodiments of the invention provide circuits and methods to operate a delay locked circuit more efficiently.
In one aspect, the delay locked circuit includes a measuring unit for obtaining a reference time based on a cycle time of an external signal during a measurement on a first path of the external signal. The delay locked circuit uses the reference time to acquire a measured delay. An adjusting unit adjusts a delay on a second path of the external signal based on the measured delay. The delay locked circuit also includes an interval controller for controlling a time interval between one measurement and the next measurement.
In another aspect, a method of processing signals includes propagating an external signal on a measuring path. A measurement is performed on the measuring path to acquire a measured delay. The method also propagates the external signal on an output path to produce an internal signal. A correction delay based on the measured delay is applied to the output path. The method further performs another measurement at a time interval unequal to the cycle time of the external signal.